WASHINGTON (AP) _ A letter sent to Senate Majority Leader Tom Daschle tested positive for anthrax on Monday as the bioterrorism scare rattling the nation reached the halls of Congress.

The discovery of anthrax in Washington followed earlier instances in Florida, New York and Nevada in which at least 12 people were exposed to spores of the potentially deadly bacteria. Monday night, another case of the disease was announced in New York.

The 7-month-old child of an ABC News employee has tested positive for anthrax, ABC News President David Westin said. The child is expected to recover. New York police commissioner Bernard Kerik said news agencies throughout the city were being inspected for anthrax contamination.

The piece of mail in Daschle's office, which contained a powdery substance, was dispatched to an Army medical research facility at Fort Detrick, Md., for further examination, said Capitol Police Lt. Dan Nichols.

The Fort Detrick findings could be available as early as Tuesday, officials said. Nichols and others warned that the initial tests were not necessarily accurate.

Bush told reporters ``there may be some possible link'' between the spate of anthrax incidents across the country and Osama bin Laden, who administration officials say was behind the Sept. 11 airline hijack attacks.

``I wouldn't put it past him, but we don't have any hard evidence,'' Bush said.

Daschle was in the Capitol and was not exposed to the letter, which was opened in his other office a block away in the Hart Senate Office Building.

Officials would not identify the person who opened the letter, though Nichols referred to the aide as a female. Aides who may have been exposed to the letter were tested with nasal swabs and being treated with the antibiotic Cipro as a precaution, said Dr. John Eisold, attending physician in the Capitol.

``They are innocent people caught up in a matter for which they have nothing to do,'' a somber-looking Daschle, D-S.D., told reporters at a news conference outside the Capitol. ``I am very, very disappointed and angered.''

Nichols said a criminal investigation led by the FBI was under way.

The Daschle letter _ and similar scares in other congressional offices _ prompted a halt to all mail deliveries in the Capitol and raised the angst there. Many lawmakers, aides and other employees already were nervous about working in a building that could be a high-profile target for terrorists.

In a further security measure, all public tours of the Capitol were halted indefinitely, Nichols said. Individual visitors will still be allowed access if they obtain passes to the visitors' galleries from their home-state lawmakers.

The suspension of the tours_ which had already been curtailed after the Sept. 11 attacks _ was planned before Monday's incident, Nichols said.

Bush's national security adviser, Condoleezza Rice, said precautions were being taken at the White House with regard to mail, but added she was not aware of any tainted letters being delivered there. Other White House aides said they've been told strict limits will be put on deliveries, including food.

``Like everybody else, we are being very cautious about what we open,'' Rice said.

In Trenton, N.J., Postal Inspector Tony Esposito and FBI officials said the letter to Daschle was postmarked in Trenton on Sept. 18, the same date and postmark on a letter that infected an NBC employee in New York last week.

Officials also were testing a female mail carrier and male maintenance worker in Trenton who reported possible symptoms of anthrax, Esposito said.

Elsewhere Monday:

_Rep. Patrick Kennedy and nine employees of his district office in Pawtucket, R.I., were taken to hospitals Monday after a worker developed a skin rash. They were released without being tested, and a hospital spokeswoman said there was no reason to believe the woman had been exposed to anthrax.

_Postal inspectors said some anthrax spores were found in the Boca Raton, Fla., post office that handled mail for American Media Inc., the tabloid publisher that lost a photo editor to anthrax. An American Media mailroom employee, who had previously tested positive for exposure, has become ill with the disease, Florida officials said.

_In Ottawa, part of Canada's federal legislature was shut down after a worker opened an envelope containing powder and developed a rash. Officials said the powder was being tested.

The letter to Daschle's office was only one of several anthrax scares at the Capitol on Monday. Sen. Frank Murkowski, R-Alaska, said his aides reported a suspicious letter and were told by Capitol Police that their report was the 12th of the day.

Aides to House Minority Leader Dick Gephardt, D-Mo., were quarantined in their Capitol suite for about 30 minutes as officers examined and removed a letter that had an international postmark and no return address. The aides said they were told the letter was not dangerous.

Daschle said about 40 people were in his office when the letter was opened Monday morning. The Capitol Police's Nichols later said about 50 people _ including officers who went to the scene _ were being tested and treated for possible exposure, and all had been sent home by mid-afternoon.

Nichols said mail to lawmakers' offices would be suspended indefinitely. Daschle's office will be closed for several days while it is cleaned, the senator said.

Staff members of Sen. Russ Feingold, D-Wis., were tested for anthrax as a precaution because they work next door to Daschle's office. All tested negative, an aide said.

Amid the activity, the Senate convened as scheduled Monday afternoon.

``This Senate and this institution will not stop,'' Daschle said on the chamber's floor. ``We will not cease our business.''